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Thursday, March 31, 2016

Bad Water, Sweet Water, and Greasewood

While traveling up the Missouri River through today’s northeast Montana, the great American explorer Meriwether Lewis came upon a shrub he didn't recognize, growing in large stands. "Hereafter I shall call it the fleshey leafed thorn” he wrote in his journal, on May 11, 1805. Lewis didn’t much like it, noting it was “extremely troublesome” and that animals avoided it (source).

For the most part, folks agree there’s little to like about greasewood, including its eponymous habitat—wet greasy mud, where vehicles slide around before becoming firmly stuck. The scientific name, Sarcobatus vermiculatus, means fleshy bramble of small worms. Indeed, greasewood branchlets develop into stiff sharp painful spines, and the succulent leaves look like little green worms. And they’re toxic, fatal to any livestock that eat them. For greasewood grows where water is bad—salty, alkali, poison.

Amazingly, greasewood appears to thrive on these harsh sites! On basin margins it grows mixed with other salt-tolerant species, but on the chemical-rich heavy soils of the lowlands, it forms pure stands where few other plants can survive.

Alkaline and saline soils present insurmountable challenges to most plants, because their roots can’t absorb water with high concentrations of solutes (dissolved chemicals). But greasewood is a halophyte—a “salt plant.” The root cells contain high concentrations of solutes, and take up water even in these difficult situations. Greasewood stores toxic salts (oxalates) in its succulent leaves, and being deciduous, disposes of them at the end of the growing season, making the soil below especially salty.

But greasewood can’t flourish on the paltry amount of water available at the surface. Fortunately it has another trick up its sleeve … or rather down its root. And this is the reason why greasewood has a fan club, albeit a small one.

• • •

Let’s walk down into a closed desert basin to a healthy stand of pure greasewood in the very bottom, and start digging.

First we have to get through heavy fine soil laced with small roots—there to absorb any water that might soak in. The networks can be dense. Donovan and colleagues (1996) found 140 km of roots per cubic meter under greasewood canopies!

Next, we dig through fine roots for several feet while navigating around substantial lateral roots 3 to 12 feet long. These are equipped with adventitious buds that send up shoots (clones) when a plant is damaged. Burned or cut plants can crown-sprout as well. No wonder the US Department of Agriculture warns land managers to leave greasewood stands alone:

“… treatment of the site will most likely fail or be a very poor investment of capital. … Areas of black greasewood that are burned, crowned, brush beat, or shallow plowed and/or shallow disked will often result in a much higher density of black greasewood. … Thus extreme caution should be exercised when selecting which sites have the best potential for improvement.” (“treatment” and “improvement” mean eradication; more details here)

By the time we’re six feet below the surface, we’ve left behind the fine roots, lateral roots and developed soil. But the tap root continues on. And it’s large—several inches in diameter:

“Near Moab, Utah, along a creek where the water had cut away the bank, exposing the roots, a greasewood 6 feet tall had roots down 18 feet, a taproot 3 inches in diameter down 6 feet, and abundant feeding roots, some 10 feet long, at a depth of 10 to 12 feet.” (Shantz 1940)

How far do we have to dig to find the tap root’s end? Usually at least 10 to 15 feet, often 20 or 30 feet, and sometimes more:

Finally the tap root reaches its destination—the blessed capillary fringe! Here root hairs absorb sweet water that has seeped up from the water table. It's sucked up the tap root 10, 20, maybe even 50 feet—whatever it takes to reach the thirsty greasewood plant, standing in hot sun on an alkali mudflat.

“These plants have been called phreatophytes. The term is obtained from two Greek roots and means a ‘well plant.’” (Meinzer 1927; arrow added).

Old timers knew that a healthy stand of greasewood meant sweet water wasn't all that far away. They knew greasewood could help them site wells. But it wasn’t until the early 1900s that ecologists and hydrologists were convinced:

“Greasewood was not at first regarded as an indicator of ground water, because to a large extent it grows on land that lies some distance above the water table. Information now at hand, however, makes it practically certain that greasewood habitually sends its well-developed taproot to considerable depths … It is, thus, one of the most trustworthy of all ground-water indicators.” (Meinzer 1929; italics added)

Groeneveld, DP. 1990. Shrub rooting and water acquisition on threatened shallow groundwater habitats in the Owens Valley, California in Proceedings: symposium on cheatgrass invasion, shrub die-off, and other aspects of shrub biology and management. Available here.

Why is it that the most annoying plants are the ones with the deepest tap roots and the ability to regenerate from damage! We've been struggling with horsetail for years now and get nowhere!!A great post, Hollis. It was interesting to read the warning about trying to 'improve' sites where greasewood grows.

Totally fascinating! I feel ashamed of complaining about the mallow taproots I've been contending with ;-) I've been thinking lately about the aromatic scent of some of the dry country plants, and now I'm curious about greasewood. Is there any fragrance to those succulent leaves?

If our greasewood, sarcobatus, is aromatic, it isn't much noticeable over the characteristic smell of alkaline and saline wetlands. Maybe I will remember to check this summer. A friend mentioned that in Arizona, Larrea is often called greasewood. Have you heard that?